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In telecommunications, a wildcard is a character that may be substituted for any of a defined subset of all possible characters. In high-frequency (HF) radio automatic link establishment, the wildcard character "?" may be substituted for any one of the 36 characters, "A" through "Z" and "0" through "9." Whether the wildcard character represents a single character or a string of characters must be specified. Computing In computer (software) technology, a wildcard character can be used to substitute for any other character or characters in a string. File and directory patterns When specifying file names (or paths) in CP/M, DOS, Microsoft Windows, and Unix-like operating systems, the asterisk pattern character ("*", also called "star") matches zero or more characters. In Unix-like and DOS operating systems, the question mark ("?") matches exactly one character; in DOS, it will also match missing (zero) trailing characters. For example, in DOS, the pattern 123??? will match 1231 or 12313, but not 1239919991. In Unix shells and Windows PowerShell, ranges of characters enclosed in square brackets ("[" and "]") match a single character within the range; for example, [A-Za-z] matches any single uppercase or lowercase letter. Unix shells allow negation of the specified character set by using a leading "!" (e.g., foo.[!ch], which will match names like foo.o). Matching wildcard patterns to multiple file or path names is referred to as globbing. Databases In SQL, wildcard characters can be used in "LIKE" expressions; the percent sign (%) matches zero or more characters, and underscore (_) a single character. Transact-SQL also supports square brackets ("[" and "]") to list sets and ranges of characters to match, a leading caret (^) matches only a character not specified within the brackets. In Microsoft Access, wildcard characters can be used in "LIKE" expressions; the asterisk sign (*) matches zero or more characters, and the question mark (?) matches a single character. Regular expressions In regular expressions, the period (".", also called "dot") is the wildcard character for a single character. Combined with the asterisk operator (.*) it will match any number of characters. |
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